Chiral cobaltI and nickel0 complexes in the synthesis of nonracemic helicenes through the enantioselective [2 + 2 + 2] cyclotrimerisation of alkynes

Abstract The enantioselective intramolecular [2 + 2 + 2] cycloisomerisation of triynes under catalysis by chiral transition-metal complexes (Co I , Ni 0 ) in order to receive nonracemic helicene derivatives was explored. The use of the chiral neomenthylindene Co I complex led to a moderate 25% ee of tetrahydro[6]helicene, which was the first example of such a reaction catalysed by the chiral Co I complex. The alternative Ni 0 catalysis employing privileged axially chiral monophosphines such as (−)-( aS )-NAPHEP led to tetrahydro[6]helicene with 64% ee, which is among the highest enantiomeric excesses so far observed for this Ni 0 -catalysed reaction.